Its a statement of the economics accounting identity I=S.

Actually, it's even more fundamental than that. If you wish to have (different, or perishable) goods/services tomorrow by forgoing them today (i.e., increase savings) you must find someone willing to do the opposite (who'd then be in debt to you). Money functions as an abstraction to hide the vast majority of this complexity.

When you lend your money to a bank (deposit it, buy a CD or bond, etc.), you become a creditor to the bank; the bank a debtor. They then lend that money to others; this the economically central function of a bank to match savers and borrowers.